Coatings derived from polyester crosslinked with melamine formaldehyde

ABSTRACT

A coating composition is based on a polyester mixed with an alkyl-etherified melamine formaldehyde. The coating composition is partially cured in a first stage to provide a thermoformable partially cured, tack-free, non-blocking, coating layer, followed by application to generally a contoured substrate and thermoforming to conform thereto. The contoured partially cured coating layer is then heat cured to form a cured coating. A hydroxyl-terminated polyoxetane containing repeat units derived from oxetane monomers having one or two pendent —CH 2 —O—(CH 2 ) n —Rf groups, wherein Rf is partially or fully fluorinated, can be esterified with polyester-forming reactants to form a fluorinated polyoxetane-modified polyester.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/492,572, filed Apr. 12, 2004, (now issued as U.S. Pat. No.7,727,436), which is a national stage entry of international patentappl. no. PCT/US03/07300, filed Mar. 5, 2003, which was acontinuation-in-part application of U.S. patent application Ser. Nos.10/091,754, filed Mar, 6, 2002 and 10/267,061, filed Oct. 8, 2002 (bothnow abandoned), which are continuation-in-part applications of U.S.application Ser. No. 09/698,554, filed Oct. 27, 2000 (now issued as U.S.Pat. No. 6,686,051), which is a continuation-in-part application of U.S.application Ser. No. 09/384,464, filed Aug. 27, 1999(now issued as U.S.Pat. No. 6,383,651), which is a continuation-in-part application of U.S.application Ser. No. 09/244,711, filed Feb. 4, 1999 (now issued as U.S.Pat. No. 6,423,418), which is a continuation-in-part application of U.S.application Ser. No. 09/035,595, filed Mar. 5, 1998 (now abandoned), thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention pertains to thermoformable coatings applied tosubstrates, and more particularly to typically two-stage heat curablecoatings applied to thermoformable substrates such as plastics. Thecoating is partially cured in a first stage to form a thermoformablecoating layer adhered to the substrate and heat cured in a second stageto additionally cure the coating and provide a hard surface coating onan article having a desired configuration.

More specifically, in a first embodiment this invention relates tofluorinated polyoxetane-polyester polymers containing polyoxetanederived from polymerizing oxetane monomers having partially or fullyfluorinated pendent side chains. Polyoxetane-polyester polymers havemany of the desirable properties of fluorinated polymers and the ease ofprocessability of polyesters. The desirable properties of thefluorinated oxetane polymers are due to the fluorinated side chains andtheir tendency to be disproportionately present at the air exposedsurface when cured. The fluorinated polyoxetane-polyester polymers arecured with an alkyl-modified melamine formaldehyde crosslinkercomprising an alkyl etherified melamine formaldehyde resin.

In a second embodiment, a coating can be made with a polyoxetane-freepolyester and cured in a multistage process. Specifically, the coatingcomprises a polyester which is cured using an alkyl-modified melamineformaldehyde crosslinking agent such as alkyl-etherified melamineformaldehyde. These polyoxetane-free compositions have a good balance ofproperties and are suitable for coating thermoformable substrates.

Thermoformable sheet substrates such as poly(vinyl chloride) (PVC) areused with polymeric coated surfaces comprising crosslinked polymers toprovide hard surfaces exhibiting considerably increased durability. Inthe past, coating integrity and hardness were achieved with varioustypes of crosslinked polymers forming a thermoset polymer network, whichworked well with flat surfaces but which had limited extensibility andelasticity and, consequently, could not be thermoformed into contoursand configurations without integrity failure (e.g., cracking). Hence,providing a crosslinked coating system for coating thermoformable sheetsubstrates (e.g., PVC) with sufficient coating integrity andextensibility to adhere while exhibiting sufficient flexibility tomaintain coating integrity during subsequent thermoforming processremains desirable.

Melamine-crosslinked polyester coatings are used in low and highpressure laminates having flat surfaces. High pressure laminatestypically consist of a multilayer paper impregnated with melamine-basedcoatings, where the impregnated laminate is cured at relatively hightemperature and pressure to produce a finished article having a hard anddurable surface. Examples of this approach include a plasticized PVClayer having a surface coating that includes (i) a reactivecarboxyl-functional polyester crosslinked with alkylated benzoguanamine,urea or melamine formaldehyde resin or (ii) a water-based polyestercrosslinked with an acid-catalyzed amino resin.

Oxetane polymers with pendent fluorinated chains have low surfaceenergy, high hydrophobicity, oleophobicity and a low coefficient offriction.

Various oxetane monomers and polymers are described in, e.g., U.S. Pat.Nos. 5,650,483; 5,468,841; 5,654,450; 5,663,289; 5,668,250, and5,668,251, and the interested reader is directed to these for moreinformation.

SUMMARY OF THE INVENTION

A coating having desirable properties for many applications can beprovided from a composition that includes a polyester and a melamineformaldehyde, more specifically a polyester reacted with analkyl-etherified melamine formaldehyde which can have one or more lower(e.g., C₁-C₆) alkyl groups or etherified substituents such as methylolor butylol groups. The composition is partially cured so as to yield anon-tacky surface and subsequently more fully cured into a thermoformed,contoured surface. This two-step curing process includes a lowtemperature stage in which a partially cured thermoformable polymericcoating layer is applied to a substrate so as to form a laminatefollowed by a second higher temperature stage in which the laminate isthermoformed into a desired (e.g., three dimensional) configurationduring which the alkyl-etherified melamine formaldehyde/polyestermixture is more fully cured and crosslinked so as to form a hard surfacecoating.

The polyester can be modified with a fluorinated polyoxetane. This typeof modified polyester can be used in the same manner as just describedso as to provide a composition from which useful coatings can be made ina two-stage curirig process. The fluorinated polyoxetane-modifiedpolyester can contain minor amounts of hydroxy-terminated polyoxetanecopolymerized polyester reactants to provide a polyester containing fromabout 0.1 to about 10% by weight copolymerized-fluorinated polyoxetanein the fluorinated polyoxetane-polyester.

DETAILED DESCRIPTION

The present composition, which includes an alkyl-etherified melamineformaldehyde and a reactive polyester (optionally fluorinatedpolyoxetane-modified), can provide a thermoformable coating whenpartially cured and a thermoformed, contoured coating when fully cured.

The thermoformable coating can be applied to, e.g., thermoformablesubstrates. Examples of useful substrates that can be coated includecellulosic products (e.g., coated and uncoated paper), fibers andsynthetic polymers including PVC, polyester, olefin (co)polymers,polyvinyl acetate, and poly(meth)-acrylates and similar thermoformableflexible, semi-rigid, or rigid substrates. Substrates can be used withor without backings and, if desired, can be printed, embossed, orotherwise decorated. Substrates also can have applied thereto one ormore intermediate coating(s) to provide a mono- or multi-chromatic orprinted (patterned) background. Also, the substrate film or layer can besmooth or can be embossed to provide a pattern or design for aestheticor functional purposes.

A thermoformed coated plastic substrate can be applied to a preformed,contoured (i.e., three dimensional) solid structure or article, such aswood, to form a laminated article of a high draw or contoured article.Exemplary articles include contoured cabinet doors, decorative formedperipheral edges on flat table tops, and similar contoured furnitureconfigurations, as well as table tops and side panels, desks, chairs,counter tops, cabinet drawers, hand rails, moldings, window frames, doorpanels, and electronic cabinets such as media centers, speakers, and thelike.

The cured coatings retain their integrity free of undesirable cracking.They also exhibit improved extensibility during the thermoforming stepand have significantly improved durability, chemical resistance, stainresistance, scratch resistance, water stain resistance, and similar marresistance characteristics. They also provide good surface gloss controlto the final laminated product.

The two stage temperature curing process is largely dependent on thesoftening point of the thermoformable substrate. A wet coating isapplied to a substrate (e.g., plastic) and dried to form a composite ofdried coating on the substrate. The composite is partially cured atrelatively low temperatures to form a thermoformable laminate ofpartially cured coating adhered to the substrate. The first stagepartial curing temperatures are at web temperatures of no more thanabout 82° C. (180° F.), desirably between about 49° and about 77° C.(120°-170° F.), and preferably between about 66° and about 71° C.(150°-160° F.). Dwell time is broadly between about 2 and about 60seconds, preferably between about 10 and about 20 seconds, depending onthe partial curing temperature. The first stage partial curing providesa thermoformable polymeric coating while avoiding thermosettingcrosslinking. The thermoformable laminate can be thermoformed into adesired contour or shape. The intermediate thermoformable coating isadvantageously extensible and preferably exhibits at least about 150%elongation at 82° C. (180° F.) after the first curing step. Generally,the first partial curing is about 70 to about 80% of the full cure of afully cured coating. The resulting thermoformable laminate is non-tacky,avoids blocking or adhesion between adjacent surface layers when rolledor stacked in sheets, and further avoids deformation due to accumulatedweight during rolling or stacking.

In the second stage, the thermoformable laminate can be applied to thesurface(s) of a three dimensional article or structural form withestablished contours, draws, or configurations and fully cured at webtemperatures of at least 83° C. (181° F.), preferably from about 88° toabout 149° C. (190°-300° F.), to provide a hard, fully cured,crack-free, mar resistant coating. Dwell time is broadly between about30 and about 300 seconds depending on the curing temperature. Curedcoatings exhibit MEK resistance of at least about 50 rubs and preferablyat least about 75 rubs. Two stage, step-wise curing can be achieved intwo or more multiple heating steps to provide, sequentially, partialcuring and full curing. Preferably, the final products are articles offurniture such as cabinets, desks, chairs, tables, molding, shelves,doors, or housings such as for appliances, or electronic components. Thecontoured structural article can be a solid substrate, such as anunfinished contoured desktop where the thermoformable laminate iscontoured, thermoset, and adhered directly to the contoured solidarticle. Alternatively, the form can be a mold for forming a freestanding thermoset contoured laminate adapted to be adhered subsequentlyto an unfinished contoured article. The fully cured surface exhibitsconsiderable mar resistance along with other cured film integrityproperties.

Returning to the composition from which the coating is derived, modifiedamino resins comprising a lower alkyl-etherified melamine formaldehydeare utilized to crosslink the polyester, regardless of whether thelatter is fluorinated polyoxetane modified. The melamine formaldehyderesin is generally etherified with one or more groups derived from analkyl alcohol. Preferred alkyl etherified melamine formaldehyde resinscomprise mixed alkyl groups in the same melamine formaldehyde molecule.Mixed alkyl groups comprise at least two different C₁-C₆ (preferablyC₁-C₄) alkyl groups, for example, methyl and butyl. Preferred mixedalkyl groups comprise at least two alkyl chains having a differential ofat least 2-carbon atoms such as methyl and propyl, and preferably a3-carbon atom differential such as methyl and butyl. Melamineformaldehyde molecules ordinarily involve a melamine alkylated with atleast three, more typically with four or five and most typically withsix, formaldehyde molecules to yield methanol groups, e.g.,hexamethylolmelamine. At least two, desirably three or four, andpreferably five or six of the methanol groups are etherified. A melamineformaldehyde molecule can contain mixed alkyl chains etherified alongwith one or more non-etherified methanol groups (known as methylolgroups), although fully etherified groups are preferred to provideessentially six etherified alkyl groups. Some of the melamineformaldehyde molecules in a melamine formaldehyde can be non-alkylatedwith formaldehyde (i.e., iminom radicals), but preferably this iscontrolled to avoid undesirable rapid premature curing and to maintainthe controlled two-stage crosslinking as described above.

Mixed alkyl etherified melamine formaldehyde crosslinking resins can beproduced in much the same way as conventional mono-alkyl etherifiedmelamine formaldehyde is produced where subsequently all or mostmethylol groups are etherified, such as in hexamethyoxymethylmelamine(HMMM). A mixed alkyl etherified melamine formaldehyde can be producedby step-wise addition of two different lower alkyl alcohols or bysimultaneous coetherification of both alcohols, with step-wiseetherification being preferred. Typically lesser equivalents of thefirst etherified alcohol relative to the available methylol equivalentsof melamine formaldehyde are utilized first to assure deficient reactionof alkyl alcohol with available formaldehyde groups, while excessequivalents of the second alcohol are reacted relative to remainingequivalents of formaldehyde to enable full or nearly full etherificationwith both alcohols. In either or both alcohol etherification steps,reaction water can be removed by distillation, or by vacuum ifnecessary, to assure the extent of coetherification desired.

A preferred commercially available amino crosslinker is Resimene™ CE-7103 resin (Solutia Inc.; St. Louis, Mo.) which is a mixed methyl andbutyl alcohol etherified with melamine formaldehyde. This preferredalkyl-etherified melamine formaldehyde exhibits temperature sensitivecuring where reactivity is in two stages to provide a partially curedthermoformable laminate which can be more fully cured at highertemperatures so as to provide a hard surface.

A fluorinated polyoxetane-polyester generally is a block copolymercontaining a preformed fluorine-modified polyoxetane having terminalhydroxyl groups. Hydroxyl-terminated polyoxetane prepolymers comprisepolymerized repeat units of an oxetane monomer having a pendent—CH₂O(CH₂)_(n)Rf group prepared from the polymerization of oxetanemonomer with fluorinated side chains. These polyoxetanes can be preparedas described in the previously mentioned patents.

The oxetane monomer desirably has the structure

wherein n is an integer of from 1 to 5, preferably from 1 to 3; Rfindependently is a linear or branched, preferably saturated, alkyl groupof from 1 to about 20, preferably 2 to about 10, carbon atoms with atleast 25, 50, 75, 85, 95, or preferably 100% having the H atoms of theRf replaced by F; and R is H or C₁-C₆ alkyl group. The polyoxetaneprepolymer can be an oligomer or a homo- or co-polymer.

The repeating units derived from the oxetane monomers desirably have thestructure

where n, Rf, and R are as described above. The degree of polymerizationof the fluorinated oxetane can be from 6 to 100, advantageously from 10to 50, and preferably 15 to 25.

A hydroxyl-terminated polyoxetane prepolymer comprising repeat units ofcopolymerized oxetane monomers ordinarily have two terminal hydroxylgroups. Useful polyoxetanes desirably have a number average molecularweight (M_(n)) of from about 100 to about 100,000, preferably from about250 to about 50,000, and more preferably from about 500 to about 5000,and can be a homo- or co-polymer of two or more different oxetanes. Thepolyoxetane prepolymer may be a copolymer including very minor amountsof non-fluorinated C₂-C₄ cyclic ether molecules such as tetrahydrofuran(THF) and one or more oxetane monomers. Such a copolymer may alsoinclude very minor amounts of copolymerizable substituted cyclic etherssuch as substituted THF. In some embodiments, the hydroxyl-terminatedpolyoxetane prepolymer can include up to 10%, advantageously from 1 to5%, and preferably from 2 to 3% copolymerized THF based on the weight ofthe preformed hydroxyl terminated polyoxetane copolymer. A preferredpolyoxetane prepolymer contains two terminal hydroxyl groups to bechemically reacted and bound into the polyoxetane-polyester polymer.

Fluorinated polyoxetane-polyester polymers can be made by a condensationreaction, usually with heat in the presence of a catalyst, of thepreformed fluorinated polyoxetane with a mixture of at least onedicarboxylic acid or anhydride and a dihydric alcohol. The resultingfluorinated polyoxetane-polyester is a statistical polymer and maycontain active H atoms, e.g., terminal carboxylic acid and/or hydroxylgroups for reaction with the alkyl-etherified melamine formaldehydecrosslinking resin. The ester forming reaction temperatures generallyrange from about 110° to about 275° C., and desirably from about 215° toabout 250° C., in the presence of suitable catalysts such as 0.1%dibutyl tin oxide. Those wishing further details on and examples of theformation of such (co)polymers are directed to, e.g., U.S. Pat. No.6,383,651 and PCT publication WO 02/34848.

Preferred carboxylic acid reactants are dicarboxylic acids andanhydrides. Examples of useful dicarboxylic acids include adipic acid,azelaic acid, sebacic acid, cyclohexanedioic acid, succinic acid,terephthalic acid, isophthalic acid, phthalic anhydride and acid, andsimilar aliphatic and aromatic dicarboxylic acids. A preferred aliphaticdicarboxylic acid is adipic acid and a preferred dicarboxylic aromaticacid is isophthalic acid. Generally, the aliphatic carboxylic acids havefrom about 3 to about 10 C atoms, while aromatic carboxylic acidsgenerally have from about 8 to about 30, preferably from 10 to 25, Catoms.

Useful polyhydric alcohols generally have from about 2 to about 20carbon atoms and 2 or more hydroxyl groups, with diols being preferred.Examples of useful polyols, include ethylene glycol, propylene glycol,diethylene glycol, dipropylene glycol, glycerin, butylene glycol, higheralkyl glycols such as neopentyl glycol, 2,2-dimethyl-1,3-propanediol,trimethylol propane, 1,4-cyclo-hexanedimethanol, glycerolpentaerythritol, trimethylolethane. Mixtures of polyols andpolycarboxylic acids can be used where diols and dicarboxylic acidsdominate and higher functionality polyols and polyacids are minimized.An example of a preferred reactive polyester is the condensation productof trimethylol propane, 2,2-dimethyl-1,3-propanediol,1,4-cyclohexanedimethanol, isophthalic acid or phthalic anhydride, andadipic acid.

The polyester component can be formed by reacting the ester-formingreactants in the presence of a preformed intermediate fluorinatedpolyoxetane oligomer, polymer, or copolymer to provide an ester linkagederived from esterifying a dicarboxylic acid or anhydride with thepreformed polyoxetane. Alternatively, a preformed polyester intermediatecan be formed from diols and dicarboxylic acids and reacted with thepreformed fluorinated polyoxetane oligomer or (co)polymer to form theester linkage between the respective preformed components. Thus, blockcopolymers are generally formed.

In preparing the hydroxyl- or carboxyl-functional polyoxetane-polyesterpolymer, it is preferred to pre-react the hydroxyl-terminatedfluorinated polyoxetane oligomer or (co)polymer with dicarboxylic acidor anhydride to assure copolymerizing the fluorinated polyoxetaneprepolymer into polyester via an ester linkage which increases thepercentage of fluorinated polyoxetane prepolymer incorporated. Apreferred process to form the ester linkage comprises reacting thehydroxyl terminated fluorinated polyoxetane prepolymer with excessequivalents of carboxylic acid from a linear C₃-C₃₀ dicarboxylic acidsuch as malonic acid, succinic acid, glutaric acid, adipic acid, pimelicacid, maleic acid, fumaric acid, or cyclic cyclohexanedioic acid, underconditions effective to form a polyoxetane ester intermediate from thehydroxyl groups of the polyoxetane prepolymer and the carboxylic acidgroups of the dicarboxylic acid or anhydride. More desirably, the excessof carboxylic acid groups is at least 2.05 or 2.1 equivalents reactedwith one equivalent of hydroxy-terminated polyoxetane prepolymer toprovide a predominantly carboxyl-terminated intermediate prepolymer. Ina preferred embodiment for producing the ester intermediate prepolymer,the amount of other diols is small to force the carboxylic acid groupsto react with the hydroxyl groups of the fluorinated polyoxetaneprepolymer. Desirably, the equivalents of hydroxyls from other diols areless than 0.5, more desirably less than 0.2 and preferably less than 0.1per equivalent of hydroxyls from the fluorinated polyoxetane prepolymeruntil after at least 70, 80, 90, or 95% of the hydroxyl groups of thepolyoxetane prepolymer are converted to ester links by reaction with thedicarboxylic acid.

The reaction temperature is generally from about 110° to about 275° C.and desirably from about 215° to about 250° C.

The preferred carboxylic acid functional polyoxetane intermediate thencan be reacted with other diol and dicarboxylic acid reactants to formthe polyoxetane-polyester polymer. Although excess hydroxyl or carboxylequivalents can be utilized to produce either hydroxyl- orcarboxyl-functional polyoxetane-polyester, preferably excess hydroxylequivalents are copolymerized to provide a hydroxyl terminatedpolyoxetane-polyester. Polyoxetane repeating units are usuallydisproportionately present at the surface of the coating due to the lowsurface tension of those units.

While not as desirable, an alternative route of reacting thehydroxyl-terminated fluorinated polyoxetane oligomer or (co)polymer isdirectly with a preformed polyester. In this procedure, the variouspolyester forming diols and dicarboxylic acids are first reacted to forma polyester block which then is reacted with a polyoxetane prepolymer.

The amount of fluorinated polyoxetane copolymerized in thepolyoxetane-polyester is desirably from about 0.1 to about 10%,advantageously from about 0.5 to about 5%, and preferably from 0.5 toabout 3% by weight based on the weight of the fluorinatedpolyoxetane-polyester. If the hydroxyl terminated poly-oxetaneprepolymer includes a significant amount of copolymerized comonomerrepeat units from THF or other cyclic ether, the hydroxyl terminatedpolyoxetane prepolymer weight can exceed the level of copolymerizedoxetane repeating units noted immediately above by the amount of othercopolymerized cyclic ether other than oxetane used to form thepolyoxetane copolymer.

The polyester as described above can contain relatively small amounts,or be substantially or completely free, of any fluorinated polyoxetaneblock. The amount of fluorinated polyoxetane therein is generally lessthan about 2 or about 1% by weight, desirably less than about 0.5 orabout 0.1% by weight, and preferably completely free of any fluorinatedpolyoxetane based upon the total weight of the polyester. The polyesterswhich are utilized are the same as set forth hereinabove and are made inthe same manner.

A preferred polyester resin is supplied by Eastman Chemical Co.(Kingsport, Tenn.) under the trade designation Polymac™ 57-5776, whichis an oil free polyester polyol having an equivalent weight of about 315and a hydroxyl number of about 178. Such polyesters generally have aM_(n) of from about 300 to about 25,000, desirably from about 500 toabout 12,000, preferably from about 750 to about 5,000, and morepreferably from about 1500 to about 2500.

The amount of the various components in the coating will be generallyspecified in relationship to 100% by weight of resin solids of thepolyoxetane-polyester or of the polyester resin polymer and the alkyletherified melamine formaldehyde. The weight percent of alkyl etherifiedmelamine formaldehyde crosslinking agent in the coating is at least 10%,desirably from about 10 to about 80%, preferably from about 20 to about70% and most preferably from about 40 to about 60% by weight of theresin binder solids of the coating composition, with the balance beingfluorinated polyoxetane-polyester polymer or in the second embodimentthe polyester polymer.

The crosslinking reaction can be catalyzed with, for example,para-toluene sulfonic acid (PTSA) or methyl sulfonic acid (MSA). Otheruseful acid catalysts include boric acid, phosphoric acid, sulfate acid,hypochlorides, oxalic acid and ammonium salts thereof, sodium or bariumethyl sulfates, sulfonic acids, and the like. Other potentially usefulcatalysts include dodecyl benzene sulfonic acid (DDBSA), amine-blockedalkane sulfonic acid such as MCAT 12195 catalyst (ATOFINA Chemicals,Inc.; Philadelphia, Pa.), amine-blocked dodecyl para-toluene sulfonicacid such BYK 460 catalyst (BYK-Chemie USA; Wallingford, Conn.), andamine-blocked dodecyl benezene sulfonic acid such as Nacure™ 5543catalyst (King Industries, Inc.; Norwalk, Conn.). Ordinarily from about1 to about 15% and preferably about 3 to about 10% acid catalyst is usedbased on alkyl-etherified melamine formaldehyde and polyester resinused.

The amount of catalyst should effectively catalyze the partial curing ofthe polyester and alkyl-etherified melamine formaldehyde resins in thetwo stages.

The amount of carriers and/or solvent(s) in the coating composition canvary widely depending on the coating viscosity desired for applicationpurposes, and solubility of the components in the solvent. Thesolvent(s) can be any conventional solvent for polyester and melamineformaldehyde crosslinker resin systems. These carriers and/or solventsinclude C₃-C₁₅ ketones, e.g., MEK or methyl isobutyl ketone; C₃-C₂₀alkylene glycols and/or alkylene glycol alkyl ethers; acetates(including n-butyl and n-propylacetates) and their derivatives; ethylenecarbonate; etc. Suitable alcohol solvents include C₁-C₈monoalcohols suchas methyl, ethyl, propyl, butyl alcohols, as well as cyclic alcoholssuch as cyclo-hexanol. More information on such carrier and/or solventsystems can be found in, e.g., U.S. Pat. Nos. 4,603,074; 4,478,907;4,888,381 and 5,374,691. The amount of solvent(s) can vary from about 20to about 400 parts by weight (pbw) per 100 pbw of total polyester andetherified melamine formaldehyde crosslinker resin solids.

Conventional flattening agents can be used in the coating composition inconventional amounts to control the gloss of the coating surface to anacceptable value. Examples of conventional flattening agents include thevarious waxes, silicas, aluminum oxide, alpha silica carbide, etc.Amounts desirably vary from about 0 to about 10, preferably from about0.1 to about 5, pbw per 100 pbw total of resin solids.

Additionally, other conventional additives can be formulated into thecoating composition for particular applications. For example,polysiloxanes can be used to improve scratch and mar resistance. Thismay be particularly advantageous where the polyester is not modifiedwith a fluorinated polyoxetane. In particular, a suitable polysiloxanecan be polyether-modified alkyl polysiloxane including, for example,BYK™ 33 polyether-modified dimethylpolysiloxane copolymer (BYK-ChemieUSA). Other examples of additives include viscosity modifiers,antioxidants, antiozonants, processing aids, pigments, fillers,ultraviolet light absorbers, adhesion promoters, emulsifiers,dispersants, solvents, cross-linking agents, and the like.

EXAMPLES Example 1 Synthesis of Fluorinated Polyoxetane-PolyesterPolymers

Two hydroxyl-terminated fluorinated polyoxetanes were used to preparedifferent polyoxetane-polyester polymers. The first polyoxetane had 6mole percent repeating units from THF with the rest of the polymer beinginitiator fragment and repeating units from3-(2,2,2-triftuoroethoxylmethyl)-3-methyloxetane, i.e., 3-FOX (n=1,Rf=CF₃, and R=CH₃ in the formulas above) and had a M_(n) of 3400. Thesecond polyoxetane had 26 mole percent repeating units from THF with theresidual being the initiator fragment and repeating units from 3-FOX.

The first and second fluorinated oxetane polymers were reacted with atleast a 2(generally 2.05-2.10) equivalent excess of adipic acid in areactor at 235° C. for 3.5 hours to form a polyoxetane having the halfester of adipic acid as carboxyl end groups. (The preformed esterlinkage and terminal carboxyl groups were used to bond the polyoxetaneto a subsequently in situ-formed polyester.) NMR analysis was used toconfirm that substantially all the hydroxyl groups on the polyoxetanewere converted to ester groups. The average degree of polymerization ofthe first oxetane polymer was reduced from 18 to 14 during the reactionwith adipic acid. The average degree of polymerizations of the secondoxetane polymer remained at 18 throughout the reaction. The reactantswere then cooled to about 149° C.

The adipic acid-functionalized polyoxetane was reacted with additionaldiacids and diols to form polyester blocks. The diacids were used inamounts of 24.2 pbw adipic acid and 24.5 pbw isophthalic acid orphthalate anhydride. The diols were used in amounts of 20.5 pbwcyclohexanedimethanol, 14.8 pbw neopentyl glycol, and 16.0 pbwtrimethylol propane. The relative amounts of the adipate ester of theoxetane polymer and the polyester-forming components were adjusted toresult in polyoxetane-polyesters with either 2 or 4 weight percent ofpartially fluorinated oxetane repeating units. The diacid and diolreactants were reacted in the same reactor used to form thecarboxyl-functional polyoxetane but the reaction temperature was loweredto about 216° C. The reaction to form the polyoxetane-polyester polymerwas continued until the calculated amount of water was generated.

Example 2 Preparation and Testing of Coated Laminate Using a FluorinatedPolyoxetane-Modified Polyester

The following ingredients were mixed and allowed to react:

Resimene ™ CE-7103 methyl/butyl- 31.4 pph  etherified melamineformaldehyde resin poly-5-FOX/polyester 31.4 pph  n-propyl acetate 20.7pph  THF 3.5 pph isopropyl alcohol 6.0 pph p-toluene sulfonic acid 4.0pph BYK ™-333 polyether-modified 0.7 pph dimethylpolysiloxane copolymerAcematt ™ TS100 fumed silica (Degussa 1.4 pph Corp.; Fairlawn, Ohio)Polyfluo ™ 190 fluorocarbon wax (Micro 0.9 pph Powders, Inc.; Tarrytown,New York)

The poly-5-FOX/polyester polymer was made from a 5-FOX polymer (madesimilarly to the 3-FOX polymer described in Example 1) reacted withadipic acid to form an ester linkage having a terminal carboxyl groupand, subsequently, with ester-forming monomers in a manner substantiallyas set forth in Example 1(with the acids being adipic acid and phthalateanhydride). Polyether-modified dimethylpolysiloxane copolymer andfluorocarbon wax were added to improve scratch and mar resistance, andfumed silica was added to control gloss.

Coatings were applied by gravure coating to 0.0305 cm (0.012 inch) thickPVC substrate sheets having a lightly embossed surface (E13 embossing).The resulting coated samples were dried in a forced air oven andpartially cured at about 66° to 71° C. (150°-160° F.) for 10 to 20seconds to form partially cured thermoformable laminates. Coatingweights were 6-8 g/m² of substrate.

The laminates were thermoformed to MDF wood board using a membranepress. Coated PVC and laminate sequentially are placed over a MDF board.The membrane was heated to about 138° C. before being pulled tightlyaround the PVC film and MDF board by vacuum (thermoforming). (Themaximum surface temperature of the PVC can be measured and recorded witha temperature indicating tape.) Heat was maintained for about a minutebefore being removed, and the membrane allowed to cool for 1 minutewhile vacuum was maintained.

The following test procedures were used to measure coating properties:

-   -   Scratch Resistance: Measured with a “Balance Beam Scrape        Adhesion and Mar Tester” (Paul N. Gardner Co., Inc.; Pompano        Beach, Fla.). A Hoffman stylus was used to scratch the coatings.        Scratch resistance is the highest stylus load the coating can        withstand without scratching.    -   Burnish Mar: Determined by firmly rubbing a polished porcelain        pestle on the coating surface. The severity of a mark is        visually assessed as:        -   Severe—mark visible at all angles        -   Moderate—mark visible at some angles        -   Slight—mark visible only at grazing angles        -   None—no perceivable mark    -   Solvent Resistance: A cloth towel was soaked with MEK and gently        rubbed on the coated surface in a back and forth manner, with        one back-and-forth movement counting as one rub. The coated        surface was rubbed until the sooner of a break in the coating        surface first becoming visible or 100 rubs.    -   Coating Crack: Corners and edges were visually inspected for        cracks in the coating.    -   Cleanability/Stain: Measured by common household substances        published by NEMA Standards Publications LD-3 for High Pressure        Decorative Laminates. The method consists of placing a spot of        each test reagent on a flat surface of the laminated article and        allowed to sit undisturbed for 16 hours. At that time, the        stains were cleaned with different stain removers that are        commonly used as commercial cleaners (e.g., Formula 409™,        Fantastik™, etc.), baking soda, nail polish remover, and finally        bleach. Depending on the difficulty (high values) or ease (low        values) of removal, the total value from each test sample was        determined.

Grade water 0 commercial cleaner 1 commercial cleaner + baking soda 2nail polish remover 3 5.0% solution of sodium hypochlorite (bleach) 4

TABLE 1 Durability Testing Coated and Coated and Fully Cured PartiallyCured Uncoated Hoffman Scratch 2050 g 1850 g 1000 g Burnish Mar SlightSlight Moderate Solvent resistance 90 rubs 60 rubs 4 rubs Coating crackNone None None

The results of Table 1 indicate that the coated samples exhibitsignificantly greater Hoffman scratch and burnish mar resistances thanuncoated PVC, and the fully cured (thermoformed) sample had betterresistance than the non-fully cured sample. Similarly, the burnishresistances of the thermoformed and coated samples were greater thanthat of the uncoated PVC.

Stain remover values as described above were used in a progressiveintensity stain-removing test scale. A “1” in the test result set forthin Tables 2a-2c indicates the stain was not removed until a strongerstain remover was used.

TABLE 2a NEMA Stain Test Results (Coated + Fully Cured) CleaningReagents 1 2 3 4 5 Score Stain acetone 1 1 1 1 1 5 Moderate coffee — tea1 1 mustard 1 1 1 3 10% iodine 1 1 permanent marker 1 1 1 3 #2 pencil 11 wax crayon 1 1 shoe polish 1 1 Total 16

TABLE 2b NEMA Stain Test Results (Coated and Partially Cured) CleaningReagents 1 2 3 4 5 Score Stain acetone 1 1 1 1 1 5 Moderate coffee — tea1 1 mustard 1 1 2 10% iodine — permanent marker 1 1 1 3 #2 pencil 1 1wax crayon 1 1 shoe polish 1 1 Total 14

TABLE 2c NEMA Stain Test Results (Uncoated PVC) Cleaning Reagents 1 2 34 5 Score Stain acetone 1 1 1 1 1 5 Moderate coffee 1 1 2 tea — mustard1 1 1 3 10% iodine 1 1 permanent marker 1 1 1 1 1 5 Moderate #2 pencil 11 2 wax crayon 1 1 2 shoe polish 1 1 1 3 Total 23

Example 3 Preparation and Testing of Coated Laminate Using an UnmodifiedPolyester

The following ingredients were mixed and allowed to react:

Resimene ™ CE-7103 methyl/butyl- 31.4 pph  etherified melamineformaldehyde resin Polymac ™ 57-5776 polyester resin 31.4 pph  n-propylacetate 20.7 pph  THF 3.5 pph isopropyl alcohol 6.0 pph p-toluenesulfonic acid 4.0 pph BYK ™-333 polyether-modified 0.7 pphdimethylpolysiloxane copolymer Acematt ™ TS100 fumed silica 1.4 pphPolyfluo ™ 190 fluorocarbon wax 0.9 pph

As in Example 2, polyether-modified dimethylpolysiloxane copolymer andfluorocarbon wax were added to improve scratch and mar resistance, andfumed silica was added to control gloss.

Coatings were applied with a #5 wire wound drawdown bar to 0.0305 cm(0.012 inch) thick PVC substrate sheets having a lightly embossedsurface (E13 embossing). The resulting coated samples were dried in alaboratory oven at about 66° C. (150° F.) for 30 seconds to formpartially cured thermoformable laminates.

These laminates were thermoformed in the same manner as in Example 2.Testing was performed as described in Example 2.

TABLE 3 Durability Testing Hoffman Scratch 3000 g Burnish Mar NoneSolvent resistance 80 Coating crack None

TABLE 4 NEMA Stain Test Results Cleaning Reagents 1 2 3 4 5 Score Stainacetone 1 1 1 1 1 5 Moderate tea 1 1 2 mustard 1 1 1 3 10% iodine 1 1 13 permanent marker 1 1 1 3 #2 pencil 1 1 wax crayon 1 1 shoe polish 1 12 Total 20

Overall, the unmodified polyester sample showed good solvent resistanceand durability (scratch and mar), although stain resistance was slightlypoorer than the fluorinated polyoxetane-modified polyester sample.

We claim:
 1. A method of providing a sheet capable of being thermoformedinto an exterior surface layer of an article, said method comprising: a)applying a composition to a substrate so as to form a composite thatcomprises a layer of said composition coating a surface of saidsubstrate, said composition comprising 1) a polyester, 2) analkyl-etherified melamine formaldehyde compound and, based on thecombined weight of the polyester and alkyl-etherified melamineformaldehyde compound, 3) from about 1 to about 15% of a thermallyactivatable catalyst; b) heating said composite to a temperature of fromabout 49° to about 77° C. for about 2 to about 60 seconds so as topartially cure said composition, thereby making said composition layernon-tacky, thereby providing a thermoformable sheet suitable for formingan exterior, outward facing surface of said article upon applicationthereto.
 2. The method of claim 1 wherein said thermo-formable sheet issuitable for forming an exterior, outward facing surface of a non-planararticle.
 3. The method of claim 1 wherein said substrate comprisespoly(vinyl chloride).
 4. The method of claim 1 wherein said polyestercomprises fluorinated polyoxetane units.
 5. The method of claim 4wherein said polyester further comprises a C₂-C₄ cyclic ether repeatingunit.
 6. The method of claim 4 wherein each of said fluorinated oxetaneunits comprises a pendent —CH₂O(CH₂)_(n)Rf group where n is an integerof from 1 to 3 inclusive.
 7. The method of claim 1 wherein saidcomposite is heated to a temperature of from about 66° to about 71° C.8. The method of claim 1 wherein said composite is heated for about 10to about 20 seconds.
 9. The method of claim 1 wherein the partiallycured composition exhibits at least about 150% elongation when measuredat 82° C.
 10. The method of claim 1 wherein said alkyl-etherifiedmelamine formaldehyde compound of said composition comprises thereaction product of a melamine formaldehyde and at least two C₁-C₆ alkylalcohols.
 11. The method of claim 10 wherein said at least two C₁-C₆alkyl alcohols comprise two alcohols having at least a two carbon atomdifferential in their chain lengths.
 12. The method of claim 11 whereinsaid at least two C₁-C₆ alkyl alcohols comprise methanol and propylalcohol.
 13. The method of claim 10 wherein said at least two C₁-C₆alkyl alcohols comprise two alcohols having at least a three carbon atomdifferential in their chain lengths.
 14. The method of claim 13 whereinsaid at least two C₁-C₆ alkyl alcohols comprise methanol and butylalcohol.
 15. The method of claim 1 wherein said melamine formaldehyde ofsaid alkyl-etherified melamine formaldehyde compound of said compositioncomprises at least three methylol groups.
 16. The method of claim 15wherein said melamine formaldehyde of said alkyl-etherified melamineformaldehyde compound of said composition comprises at least fourmethylol groups.
 17. The method of claim 16 wherein said melamineformaldehyde of said alkyl-etherified melamine formaldehyde compound ofsaid composition comprises at least five methylol groups.
 18. The methodof claim 17 wherein said melamine formaldehyde of said alkyl-etherifiedmelamine formaldehyde compound of said composition comprises sixmethylol groups.
 19. The method of claim 15 wherein at least one of saidat least three methylol groups is alkyl etherified.
 20. The method ofclaim 15 wherein each of said at least three methylol groups is alkyletherified.